PROJECT SUMMARY/ABSTRACT Invariant natural killer T (iNKT) cells play an important role in the progression of chronic inflammatory diseases of the vasculature, including atherosclerosis and lupus-associated vascular disease. The overall goal of this application is to obtain in depth understanding of the in vivo mechanisms underlying iNKT cell activation by various stimuli and to utilize this information for the development of better therapeutic approaches of chronic inflammatory diseases of the vascular system. The investigators of this application have shown that the iNKT cell antigen -galactosylceramide (-GalCer) can prevent the development of lupus-like disease in mice, but paradoxically exacerbates the development of atherosclerosis in susceptible animals. Despite the impact of - GalCer treatment on a variety of disease processes, our understanding of the response of iNKT cells themselves to various stimuli is limited. Recent studies from the PI's laboratory have demonstrated that in vivo activation of iNKT cells with -GalCer results in a dynamic response by these cells that is characterized by surface receptor downmodulation, expansion, cytokine production, cross-talk with other cells, homeostatic contraction, and acquisition of an anergic phenotype. Guided by these preliminary findings, studies in this application will test the overall hypothesis that iNKT cells, by responding to a variety of endogenous and exogenous molecular patterns, can modulate the progression of chronic inflammatory diseases of the vascular system. This hypothesis will be tested in the following integrated Specific Aims. Aim 1 will investigate the mechanisms by which iNKT cells respond to endogenous and exogenous molecular patterns that modulate the progression of inflammatory vascular disease. These studies will be focused on identifying iNKT cell stimuli that can induce iNKT cell anergy and to investigate the role of co-stimulatory receptors in the acquisition of this anergic phenotype. Aim 2 will investigate the impact of iNKT cell anergy on the capacity of these cells to modulate chronic inflammatory vascular disease. A major goal of this aim will be to identify iNKT cell-based treatment modalities that can protect susceptible mice against the development of both lupus-like autoimmunity and atherosclerosis. Aim 3 will investigate the response of human iNKT cells to glycolipid antigens and microbial products, which will permit validation of the mouse studies. Completion of the work described in this proposal will provide novel insight into fundamental iNKT cell biology and the immunomodulatory activities of iNKT cells during the progression of vascular diseases. These studies will build a foundation of knowledge upon which safe and effective iNKT cell-based therapies for lupus, atherosclerosis and other chronic inflammatory diseases of the cardiovascular system can be developed.